In commonly assigned U.S. Pat. No. 5,229,810, incorporated herein by reference, a photographic filmstrip having a virtually transparent, magnetic film layer on the non-emulsion side of the filmstrip (referred to as an MOF layer) is disclosed in conjunction with various camera systems. One or more longitudinal read/write tracks are illustrated in the MOF layer between the side edges of the image frame area and the filmstrip where information such as film type, film speed, film exposure information and information relevant to the processing and subsequent use (e.g., printing) of the exposed image flames is pre-recorded during manufacture of the filmstrip cartridge. The camera disclosed therein is provided with a magnetic read/write head for reading out the pre-recorded information useful for controlling camera operations and for recording of information on certain other film edge tracks during camera use. The information recorded during camera use may include voiced messages or sound associated with the photographed scene and may be recorded in digital or analog format on the certain tracks.
Referring now to FIG. 1, the MOF layers on a film strip 10 in which such information may be recorded and from which pre-recorded information may be read out are depicted. The magnetically coated, color negative 35 mm film strip 10 includes a base 11, various well-known photo-chemical emulsion layers 13 on one side of the base 11 and a virtually transparent MOF layer 15 on the other side. An anti-static and lubricating layer 17 overlies the MOF layer 15. The film strip 10 includes a single perforation 19 along at least one film edge at regular intervals matching the pitch of a metering pawl in a camera adapted to use the film strip 10.
For purposes of recording data in the magnetic layer 15, each frame of the film strip 10 may be formatted as shown in FIG. 1 (as more fully described in the '310 patent, the disclosure of which is incorporated herein by reference). The frame area is divided into a plurality of predetermined longitudinal track locations designated in the drawing as outermost tracks C0-C3 and innermost tracks F00-F29. As described more fully in the '310 patent, certain of the tracks may be reserved for recording of information in the camera using magnetic recording means included in the camera. In addition, other tracks may be reserved for use by the photofinisher, and certain of the tracks may be used for recording of audio information.
In filmstrip 10, first edge tracks C0 and C1 are formed in imperforate edge region 10a and second edge tracks C2 and C3 are formed in perforate edge region 10b. In order to accommodate the presence of the camera tracks C2 and C3 along the edge region 10b, the perforations 19 are spaced to be adjacent the borders of successive image frames. In the embodiment of FIG. 1, there is only one perforation 19 in each frame border along only the edge region 10b. However, it will be understood that two perforations adjacent the beginning and the end of each image frame may be provided in edge region 10b.
In filmstrip 10, the density of the virtually transparent MOF layer 15 is much lower than in typical magnetic tape. Because of the low magnetic density of the MOF layer 15, it is of particular importance that the magnetic read/write head-to-film interface must have high compliance. Because of the MOF layer side and the emulsion side to scratching and damage, it is also important to avoid scratching the MOF layer or the emulsion layers. As a result, extreme care must be taken in the design of the components of the head-to-MOF layer interface and the backing support-to-emulsion interface to ensure that minimal surface damage occurs.
The photographic filmstrip 10 is of much greater thickness than the magnetic tape used for commercial and consumer recording and reproduction and is neither compliant nor inherently flat. When removed from its cartridge, such a filmstrip has a relatively high stiffness and very observable, positive cross-film curvature across its width that is convex on or toward the filmstrip MOF layer side as shown in the schematic end view illustration of FIG. 2. The positive cross-film curvature or curl is primarily caused by the number of emulsion layers 13 and the MOF layer 15. The emulsion and MOF layers have different stretch properties than that of the base film substrate of acetate, PET, or PEN material. The positive cross-film curvature is also influenced by the bending phenomena known as anticlastic curvature. The degree of positive cross-film curvature also depends on environmental conditions, including the time and temperature history of the film, the relative humidity, and the thickness of the film.
In addition, the unrestrained filmstrip exhibits a curvature along its length, again typically curling in on the filmstrip emulsion side. This lengthwise curl is attributed primarily to a core-set curl that results from the filmstrip having been tightly wound on a film cartridge spool.
In cameras, the cross-film and lengthwise curl of the filmstrip advanced from the cartridge through the exposure gate is flattened, at least in the image frame area, by confining the filmstrip between two edge rails and a platen as shown, for example, in commonly assigned U.S. Pat. No. 4,947,196 (FIG. 3). When the filmstrip is confined in the camera exposure gate, it is forced into an essentially planar surface in the image area to ensure that the captured image is not distorted, and the emulsion side is presented toward the imaging lens and shutter assemblies. The flattening of the filmstrip inside the rails leads to severe edge distortion or "ears" formed at the side edge regions 10a and 10b outside the rails.
FIG. 3 of the present invention shows an example of this edge ear curl in edge regions 10a and 10b which is a function of the degree of bending, humidity, and core set of the filmstrip 10. The cross-film curl of FIG. 3 is for a bend radius of 1.90" and 50% relative humidity. Each perforation 19 can locally distort the adjacent ear shape of the edge region 10b.
Because of the ears, which are a necessary byproduct in the camera environment and also occur when the filmstrip is wrapped around a magnetic head, it is difficult to achieve good contact or compliance across the width of the MOF layer tracks C0-C3 outside the image frame area. To address these problems and concerns, a number of magnetic read/write head suspensions and backing supports have been proposed for implementation in cameras. Commonly assigned U.S. Pat. Nos. 4,933,780, 4,996,546, 5,005,031, and 5,028,940, and further U.S. Pat. No. 5,307,100 disclose various miniaturized magnetic read/write head and backing support configurations for use in recording and/or reproducing in the longitudinal tracks alongside the filmstrip edges. These patents generally teach shaping the magnetic record/reproduce head as an arc section of a cylinder centered on the head gap and either flattening the filmstrip MOF layer against the head gap or wrapping the filmstrip MOF layer over the arc section to a slight degree to provide a line contact of the magnetic head gap with the MOF layer. Pressure pad supports or rollers of various configurations bearing against the filmstrip emulsion side opposite from the magnetic head and continuous motion of the filmstrip are taught to provide compliance for recording and/or reproducing information in the edge tracks. In the above-referenced '196 patent, the magnetic read/write head is suspended on a flexure arm to permit a tilt or roll of the magnetic head such that head contact with the curled ears of the filmstrip edge regions is maintained during movement of the filmstrip.
In photofinishing operations, further magnetic read and or write head assemblies are provided in association with a printer or in film preparation work station so that both the pre-recorded and the camera use recorded information will be read out for control and reprint purposes during photofinishing. Also, it is desirable for the photofinisher to have the capability to record additional information related to finishing, e.g. printing exposure conditions, customer information, reorder information, etc. in further tracks. In the photofinishing operations, the filmstrips are first developed, spliced together end-to-end and wound on film supply reels. The length of film is then advanced through a film preparation work station or photographic printer or the like to read out filmstrip information, image frame information and the magnetically recorded information. The filmstrips are advanced through filmstrip edge and image frame scanners for reading out prerecorded film information and image frame information for use in controlling printing operations or the like. In this process, it is important to maintain a steady velocity of the film to avoid scanning errors.
Again, in this case, to provide a reliable read or write signal, the length of the magnetic read and write head gaps must remain in close proximity to the tracks of the MOF layer. Any disturbances, e.g. changes in film curl in the ear region, splices and lateral offsets in the spliced filmstrips, can vary the relationship of the recording head gap to the magnetic coating and decrease the reliability of the signal. Commonly assigned U.S. Pat. Nos. 5,034,836, 5,041,933, 5,274,522, 5,285,324 and 5,285,325 disclose magnetic read/write head configurations for tracking the film edge tracks particularly for use in such photofinishing equipment. Generally, space constraints are relaxed in the photofinishing context, and the head suspension and backing support systems disclosed therein are bulkier than can be employed in cameras. These patents generally also teach shaping the magnetic read/write head surfaces as arc sections of a cylinder and either flattening the filmstrip or wrapping or conforming the filmstrip MOF layer over the arc section head surface to provide a line contact of the magnetic head gap with the MOF layer. Pressure pad supports or rollers on the emulsion side opposite from the recording heads and continuous motion of the film are taught to provide compliance for recording and/or reproducing information.
The above-referenced '522 patent discloses a flexible backing member confined in a rigid frame for a read/write head and is suggested for use in both camera and photofinishing applications. In the system disclosed therein, the cross-film curl including the ears at the filmstrip edge regions 10a and 10b is also attempted to be flattened out. In these head suspension and backing support assemblies, the attempt is made to flatten out the cross-film curl as much as possible and to adjust the assemblies to follow the filmstrip edges so that the magnetic heads remain aligned with the tracks.
Returning to FIG. 3, and summarizing the above, when a filmstrip is tensioned lengthwise and is bent around a head contour, the cross-film curl distortion present in planar form is macroscopically removed at the bend except that the ears are now present in the edge regions 10a, 10b. For a typical 100-mil-wide magnetic read/write head to conform to the edge ears of the filmstrip 10, it is necessary to provide a backing pressure on the emulsion side of the filmstrip 10 to force the film to conform to the MOF layer side as described in the above-referenced patents. These systems increase the pressure on the MOF layer and emulsion layers and impart undesirable drag that can negatively affect the ability to maintain the desired steady velocity in photofinishing equipment.
In addition, the total pressure between the magnetic head contour and the MOF layer, as a result of the required back pressure, is such that excessive and uneven wear of the head takes place on the contour. The result is that intimate compliance between the head gap and tracks in the edge regions is nonuniform rendering the system unsuitable for high density recording.